Apparatus for manufacturing bead filter

ABSTRACT

A method and an apparatus for manufacturing a bead filter for eliminating electromagnetic interference noises generated in electronic apparatuses are disclosed. The present invention improves an adhesive manufacturing process, an adhesive applying process and an adhesive drying process, so that the radial bead filters of the present invention having superior electromagnetic characteristics would be minimally affected by the adhesive, and superior bonding strengths of the radial bead filters can be maintained. The method for manufacturing the bead filter composed of a lead wire and a pair of ferrite cores for eliminating electromagnetic interferences in electronic apparatuses, includes the step of mixing 10-40 wt % of an epoxy powder and 60-90 wt % of benzyl alcohol so as to prepare an epoxy resin gel. With this epoxy resin gel, the bead filters are continuously manufactured with a simple process.

This application is a division of application Ser. No. 08/5469,799 filedOct. 23, 1995 now U.S. Pat. No. 5,851,341.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus formanufacturing a bead filter for eliminating electromagnetic interferencenoises generated in electronic apparatuses. More specifically, thepresent invention relates to a method and an apparatus for manufacturinga bead filter, in which a pair of ferrite cores and a lead wire arecontinuously coupled together without degrading the performance of theelectronic apparatus due to an adhesive layer, thereby improving theproductivity.

DESCRIPTION OF THE PRIOR ART

Generally, electromagnetic interference generated in electronicapparatus propagate through wires or through empty space, generatingnoise and causing malfunction in peripheral apparatus.

A bead filter is employed to solve the problem of electromagneticinterference. This bead filter is composed of a pair of ferrite coreseach having a through hole, and a lead wire passing through the ferritecores. The lead wire is fixed to the ferrite cores by adhesive.

Generally, the bead filter requires the following characteristics. Thatis, the bead filter should have an electromagnetic characteristics sameas the case where the adhesive is not used. The bonding strength of thecoupled ferrite core and the lead wire, which is decided by theadhesive, should be superior. Further the productivity should be alsosuperior.

That is, when the ferrite cores and the lead wire are coupled by usingthe adhesive, the bonding strength between them and the electricmagnetic characteristics of the bead filter should be same as when theadhesive is not used. Further, the productivity should be superior.

In manufacturing the bead filter, the adhesive is filled into theferrite core to fix the lead wire to the ferrite core.

Where the adhesive is filled into the ferrite core for fixing the leadwire to the ferrite core, the adhesive shrinks while being dried causinga contraction stress on the surface of the ferrite core, with the resultthat the material uniformity is aggravated. Particularly, when theadhesive is filled into the ferrite core, a core magnetic resistance isformed, with the result that the electromagnetic characteristics,particularly the impedance |Z| is lowered.

The adhesive used in manufacturing the bead filter is known to includeepoxy based adhesives, resin based adhesives, and phenol basedadhesives. If the above mentioned adhesives are used, the cost is low,and the drying time period is shortened so as to improve productivity.However, generally, they are used in the form of a solution (dippingprocess), and therefore, the contraction ratio is large compared withother adhesives. Therefore, the internal stress becomes larger. Further,the resin adheres onto the surface of the ferrite core and solidifies,with the result that the electromagnetic characteristics are extremelyaggravated. Further, the material properties of the adhesive areunstable in the frequency bands of several scores to several hundreds ofMHz (generally 50-300 MHz) and therefore, the high frequencycharacteristics are aggravated, so that product reliability cannot beassured.

When phenol based adhesives are used, there is an advantage that thecontraction stress during drying is low. However, the bonding strengthis very low and, therefore, if the lead wire is to be bonded to theferrite core, a large amount of the adhesive has to be used. Dimensionaldefects are generated and the required bonding strength value (thebonding strength between the core and the lead wire: 3-5 kgf) cannot beattained at the automatic bonding machine at the normal temperature.Therefore, the mechanical strength of the product cannot be ensured.Further, the drying time is lengthy in the relative terms and,therefore, productivity is lowered.

When epoxy based adhesives are used, the generation of theelectromagnetic radiation is low compared with other adhesives. Further,their thermosetting property is high, and therefore, the bondingstrength is high. Productivity is almost similar to the resin basedadhesives. Therefore, the epoxy based adhesives are widely used inmanufacturing the bead filter.

In addition, the bead filter for eliminating the electromagneticinterferences is classified into axial and radial types. Currently, theradial bead filters are widely used.

FIGS. 1A-1D schematically illustrates conventional methods formanufacturing the radial bead filter by using the epoxy based adhesive.

The manufacturing method of FIG. 1A is carried out in the followingmanner. First a pair of ferrite cores 12a and 12b having through holes(14a) and (14b) (see e.g. FIG. 4) are each fitted to a U shaped leadwire 10. The assembly is then lowered vertically downward so that anepoxy powder 15 adheres onto the ferrite cores 12a and 12b and the leadwire 10, thereby completing the manufacture of the bead filter.

In this method, however, prior to applying the epoxy powder 15, theferrite cores 12a and 12b and the lead wire 10 are pre-heated, and atleast three rounds or more of epoxy powder applying process have to becarried out. Therefore, the manufacturing facility and the manufacturingprocess are complicated.

Meanwhile, the manufacturing method of FIG. 1B is carried out in thefollowing manner. First, a pair of ferrite cores 12a and 12b are fittedto a U shaped lead wire 10. This assembly is then dipped into a liquidepoxy resin 16 so that the ferrite cores 12a and 12b and the lead wire10 can be bonded together, thereby completing the manufacture of thebead filter. In this method, however, when the liquid epoxy resin 16 issolidified, mechanical stresses are accumulated on the surfaces of theferrite cores 12a and 12b, so that the electromagnetic characteristicsof the finished products may be aggravated.

The manufacturing method of FIG. 1C is carried out the following manner.First, a pair of ferrite cores 12a and 12b are fitted to a U shaped leadwire 10 and a liquid epoxy resin 16 is then spread on the assembly ofthe ferrite cores 12a and 12b and the lead wire 10, thereby completingthe manufacture of the bead filter. In this method, however, theassemblies of the ferrite cores 12a and 12b and the lead wire 10 have tobe spread with the liquid epoxy resin 16 one by one, and therefore,production speed is slow.

The manufacturing method of FIG. 1D is carried out in the followingmanner. First, a ferrite core 12 is fitted to a straight lead wire 10and an epoxy resin is then spread on the assembly. Then the lead wire 10is bent into a certain contour, thereby completing the manufacture ofthe bead filter. In this method, however, the manufacturing process iscomplicated.

In the manufacturing method for the axial bead filter, an epoxy basedadhesive is used, and an endless chain is utilized to carry out acontinuous process.

In this method, the productivity is superior but the adhesive contractsduring solidification, with the result that stress is accumulated on thesurface of the ferrite core. Due to the accumulated stress, dislocationsoccur in the crystal structure of the ferrite core, so that uniformitythroughout the lattices is aggravated. Consequently, the electromagneticcharacteristics such as impedance and inductance are aggravated.

SUMMARY OF THE INVENTION

The present inventor carried out studies and experiments repeatedly toovercome the above described disadvantages of the conventionaltechniques.

Therefore it is an object of the present invention to provide a methodand an apparatus for manufacturing a bead filter, in which the adhesivemanufacturing process, the adhesive applying process and the dryingprocess are improved so as to minimize the aggravation of theelectromagnetic characteristics and to improve the bonding strength, andin which the bead filter is made to be produced in a continuous manner,so as to improve the productivity.

It is another object of the present invention to provide an apparatusfor manufacturing a bead filter, in which the productivity is improved.

In achieving the above objects, the method for manufacturing the beadfilter composed of a lead wire and a ferrite core having a through holeeach, for eliminating electromagnetic interferences in electronicapparatuses according to the present invention includes the steps of:

mixing 10-40 wt % (to be called % below) of epoxy powder and 60-90% ofbenzyl alcohol so as to prepare an epoxy resin gel;

defoaming the epoxy resin gel;

making a plurality of lead wires ready;

deciding a portion of the lead wire where the epoxy resin gel is to beapplied;

inserting each of the lead wires into each of the ferrite cores, andconveying the lead wires separated with certain intervals;

positioning each of the cores so as for the epoxy resin gel appliedportion of the lead wire not to be disposed within the through hole ofthe ferrite core;

applying the defoamed epoxy resin gel to the epoxy resin gel applyingportion of each of the continuously carried lead wires;

rotatingly moving the ferrite core up to a final position on the leadwire after passing the portion of the applied epoxy resin gel, so as toform a resin layer between the inside of the through hole and theoutside of the lead wire; and

drying the formed resin layer at a temperature of 150-400° C., wherebythe lead wire and the ferrite core are bonded together.

In another aspect of the present invention, the apparatus formanufacturing the bead filter according to the present inventionincludes:

a means for moving a lead wire inserted into a ferrite core;

a body portion for guiding and supporting the moving means;

first and second inclined plates for moving the ferrite cores in theopposite directions, and attached to the body portion;

a drying furnace installed at a side of the body portion adjacently tothe second inclined plate; and

an adhesive applying means installed between the first and secondinclined plates, for applying the adhesive to the lead wire.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object and other advantages of the present invention willbecome more apparent by describing in detail the preferred embodiment ofthe present invention with reference to the attached drawings in which:

FIG. 1 illustrates a conventional process for manufacturing the radialbead filter, in which:

FIG. 1A illustrates a process using an epoxy powder as the adhesive;

FIG. 1B illustrates another process using a liquid epoxy resin as theadhesive;

FIG. 1C illustrates still another process using a liquid epoxy resin asthe adhesive; and

FIG. 1D illustrates still another process for bend-forming the leadwire;

FIG. 2 is a partial plan view of the apparatus for manufacturing theradial bead filter according to the present invention;

FIG. 3 is a detailed illustration of the apparatus of FIG. 2, in which:

FIG. 3A is a sectional view taken along a line A--A of FIG. 2;

FIG. 3B is a sectional view taken along a line B--B of FIG. 2;

FIG. 3C is a sectional view taken along a line C--C of FIG. 2;

FIG. 3D is a sectional view taken along a line D--D of FIG. 2; and

FIG. 3E is a sectional view taken along a line E--E of FIG. 2; and

FIG. 4 is a schematic sectional view showing an example of the radialbead filter according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In manufacturing the bead filter according to the present invention,first an epoxy resin gel is prepared.

In order to prepare the epoxy resin gel, an epoxy powder in an amount of10-40% and benzyl alcohol in an amount of 60-90% are mixed together.

The epoxy powder is added to give the bonding strength, and thecomposition of the epoxy powder is as follows.

That is, the epoxy powder which is preferably employed in the presentinvention is composed of: 40-80% of resin, 10-50% of SiO₂, less than 20%of Al₂ O₃, less than 10% of Sb₂ O₃, and less than 5.0% of TiO₂, PbO, SnOand CaO (This is also called "A type epoxy powder").

Or the resin powder of the present invention is composed of: 40-80% ofresin, less than 20% of SiO₂, 10-50% of Al₂ O₃, less than 10% of Sb₂ O₃,and less than 5.0% of TiO₂, PbO, SnO and CaO (This also called "B typeepoxy powder").

Of the A type epoxy powders, the one which is preferably employed in thepresent invention is composed of: 50-70% of resin, 25-40% of SiO₂, 1-13%of Al₂ O₃, 2-5% of Sb₂ O₃, and 0.1-2.0% of TiO₂, PbO, SnO and CaO.

Of the B type epoxy powders, the one which is preferably employed iscomposed of: 50-70% of resin, 1-13% of SiO₂, 25-40% of Al₂ O₃, 2-5% ofSb₂ O₃, and 0.1-2.0% of TiO₂, PbO, SnO and CaO.

The A type and B type epoxy powders are desirably made to contain 20-70%of a resin (bisphenol A: called "BPA" below), and/or they are desirablymade to contain 1-5% of a multi functional anhydrite.

If the BPA or the multi functional anhydrite are added, the bondingstrength is reinforced.

Meanwhile, if the content of the epoxy powder is less than 10%, then theamount of benzyl alcohol which serves as a solvent is increased in therelative terms, and therefore, a sufficient bonding strength is notprovided. On the other hand, if its content is more than 40%, the solidcomponent is increased, and therefore, gellizing becomes difficult, withthe result that the viscosity becomes too high, and that thedistribution of the resin component becomes non-uniform. Therefore, itis desirable to limit the content of the epoxy powder to 10-40%.

When preparing the epoxy resin gel, a stabilizer may be desirably addedfor inhibiting the evaporation of benzyl alcohol.

The stabilizer includes acetone and ethyl alcohol, and one or both ofthem may be mixed in an amount of less than 8% in a mixture of the epoxypowder and benzyl alcohol.

If the content of the stabilizer is more than 8%, the resin in benzylalcohol is dissolved, and therefore, the viscosity is lowered.Particularly, in the case of acetone, it is bonded with the epoxy resinso as to make the polymer decomposed.

The mixing may be desirably carried out by applying a ball millingprocess. The mixing time may be 1-12 hours, and preferably 2-5 hours.The ball milling speed should be preferably 50-150 rpm, and the ball jarsize should be preferably 150-200 mm.

Meanwhile, for the epoxy resin gel prepared by mixing in the abovedescribed method, the cakes should be filtered off. The fineness of thesieve should be preferably 250 meshes or more, or preferably 250-325meshes, so that a superior filtering effect can be obtained.

Then for the epoxy resin gel prepared in the above described manner, aprocess of removing bubbles has to be carried out.

The defoaming time should be preferably 10-36 hours, and the reason isas follows. If the defoaming time is less than 10 hours, a sufficientdefoaming cannot be carried out, while if the defoaming time is morethan 36 hours, benzyl alcohol as solvent is evaporated. A morepreferable defoaming time should be 10-24 hours.

By carrying out the defoaming treatment as described above, the bondingdefects due to the expansion of bubbles can be eliminated during thedrying of the epoxy resin layer.

Meanwhile the viscosity of the epoxy resin gel should be maintainedpreferably at 30-100 cps, and the reason is as follows. If it is lessthan 30 cps, the fluidity is too large, and therefore, the epoxy resingel cannot be easily made to adhere onto the lead wire, as well as thata sufficiently thick bonding resin layer cannot be obtained. On theother hand, if the viscosity of the epoxy resin gel is more than 100cps, a bonding resin layer of a uniform thickness cannot be obtained. Amore preferable viscosity of the epoxy resin gel is 30-50 cps.

After preparing the epoxy resin gel in the above described manner, theepoxy resin gel is applied to the lead wire so as to form a bondingresin layer between the lead wire and the ferrite core. Then the bondingresin layer is dried, and this will be described in detail below.

That is, a plurality of lead wires are made ready, and then, thepositions on the lead wires on which the epoxy resin gel is to beapplied are determined.

The epoxy resin gel applying position on the lead wire is determined asfollows. That is, the epoxy resin gel is applied such that the length ofthe adhesive resin layer should be equivalent to more than 50% of thelength of the ferrite core. More preferably the epoxy resin gel isapplied such that the length of the adhesive resin layer should beequivalent to 50-90% of the length of the ferrite core.

If the length of the adhesive resin layer is less than 50% of the lengthof the ferrite core, then the length of the adhesive resin layer is tooshort, with the result that the bonding strength is too weak. If thelength of the adhesive resin layer is more than 90% of the length of theferrite core, the workability is aggravated, although the bondingstrength is superior.

Then the lead wire is inserted into the ferrite core, and such assembledlead wires and ferrite cores are continuously carried.

Then the position of the ferrite core is decided such that the bondingresin applying position would be disposed within the through hole of theferrite core.

Then the defoamed epoxy resin is applied to the above described positionon the lead wire.

Then the ferrite core is rotatingly fitted to the lead wire to the finalposition after passing the resin applied position, so that a bondingresin layer would be formed between the inside of the through hole ofthe ferrite core and the outside of the lead wire.

When the ferrite core advances toward the epoxy resin which is appliedon the lead wire, the ferrite core has to be rotatingly advanced. Thereason is as follows. That is, the epoxy resin gel has to be uniformlyspread between the inside of the through hole and the outside of thelead wire, so that a uniform bonding resin layer would be formed.

Then the bonding resin layer is dried at a temperature of 150-400° C.,so that the lead wire and the ferrite core would be firmly bondedtogether, thereby completing the manufacturing of the bead filter.

If the drying temperature is below 150° C., benzyl alcohol which is anorganic solvent remains, with the result that the bonding strength isaggravated. On the other hand, if the drying temperature is over 400°C., the epoxy resin powder is carbonized, with the result that thebonding layer becomes brittle.

A more preferable drying temperature is 250-350° C.

When drying the bonding resin layer, the drying time should bepreferably 30 seconds to 10 minutes, more preferably 1-5 minutes.

If the drying time is less than 30 seconds, a sufficient drying cannotbe realized, while if the drying time is more than 10 minutes, the epoxyresin powder is carbonized, with the result that the bonding resin layerbecomes brittle.

As to the drying method for drying the bonding resin layer, stepwiseheating zones may be desirably formed, so that a speedy evaporation ofthe organic solvent can be prevented.

As to the stepwise heating zone method, a 2-step drying zone method or a3-step drying zone method may be adopted.

The 2-step drying zone method may desirably include: a pre-heating partfor heating the bonding resin layer at a temperature of 100-250° C.; anda drying part for finally drying the bonding resin layer at atemperature of 250-400° C. The pre-heating time should be preferablyless than 8 minutes, while the drying time should be preferably 30seconds to 2 minutes.

The 3-step drying zone method may desirably include: a pre-heating partfor pre-heating the bonding resin layer at a temperature of 100-200° C.;a drying part for finally drying the bonding resin layer at atemperature of 200-400° C.; and a cooling part for carrying out acooling down to a temperature of 50-250° C. The pre-heating time shouldbe preferably 30 seconds to 4 minutes, the drying time should bepreferably 30 seconds to 2 minutes, and the cooling time should bepreferably less than 4 minutes.

In employing the stepwise drying zone method, the drying temperature andthe drying time have to be properly controlled by taking into accountthe evaporation of the organic solvent during the pre-heating, theremoving of the bubbles of the epoxy resin gel, and the carbonization ofthe epoxy resin during the drying.

Now the apparatus for manufacturing a bead filter according to thepresent invention will be described.

As shown in FIGS. 2 and 3, a radial bead filter manufacturing apparatus100 according to the present invention includes:

a conveyor 110 for conveying lead wires 10, each of the lead wire 10inserted into a pair of ferrite cores 12a and 12b;

a body portion 120 for guiding and supporting the conveying means 110;

first and second inclined plates 130 and 140 coupled to the body portion120, for moving the ferrite cores 12a and 12b in the oppositedirections;

a bonding means 150 installed between the first and second inclinedplates 130 and 140, for applying the adhesive to the lead wire 10; and

a drying furnace 160 installed at a side of the body portion 120adjacently to the second inclined plate 140.

The conveyor means 110 includes: a conveying strip 111 for conveyingassemblies of the lead wires 10 and the ferrite cores 12a and 12b; and aconveying strip moving device 112 for moving the conveying strip 111.

The conveying strip 111 includes a strip shaped base paper 1111positioned under the lead wires 10; and a tape 1112 for securing thelead wires 10 onto the base paper 1111.

On the base paper 1111 and the tape 1112, there are formed a pluralityof pin holes 1112a with certain intervals for facilitating the conveyingof the lead wires 10. The tape 1112 should be preferably a thermal tapehaving a superior adhesive strength.

The conveying strip moving device 112 is driven by a driving source (notshown), and includes a plurality of gear rollers 1121 and pin rollers1122 for moving the conveying strip 111.

The pin roller 1122 includes a plurality of pins 1122a at the sameintervals as those of the pin holes 1112a which are formed on the tape1112.

The body portion 120 includes: a first guiding part 121 for guiding theconveying strip 111; and a second guiding part 122 disposed opposinglywith the first guiding part 121, for guiding the lead wires 10.

The first guiding part 121 is expanded beyond the drying furnace 160,and includes a first guiding face 121a and a first expanding part 121b.The base paper 1111 of the conveying strip 111 is positioned on thefirst guiding face 121a, and a plurality of the gear rollers 1121 andthe pin rollers 1122 are connected to the first expanding part 121b in adrivable manner.

Further, the first guiding face 121a is provided with pin accommodatingholes 1211a for accommodating the pins 1122a of the pin rollers 1122.

Further, the second inclined plate 140 is fixed on the first guidingpart 121, for conveying the ferrite cores 12a and 12b toward the secondguiding part 122.

As shown in the enlarged portion of FIG. 2, the first expanding part121b is desirably provided with a conveying strip guide 1113 forpreventing the departure of the conveying strip 111.

At a position on the first expanding part 121b of the first guiding part121 which corresponds to between the rear end of the second inclinedplate. 140 and the leading end of the drying furnace 160, there isdesirably installed a tap holder 123.

The first guiding face 121a of the first guiding part 121 whichcorresponds to between the leading end of the tap holder 123 and therear end of the drying furnace 160 should be inclined by a certaindegree e, preferably by 20° C., as shown in FIGS. 3D and 3E.

The tap holder 123 is positioned such that it has a conveying stripretaining hole 123a, so that the conveying strip 111 can pass throughbetween the tap holder 123 and the first guiding face 121a. Thus the tapholder 123 makes the conveying strip 111 downwardly inclined.

That is, the conveying strip 111 which passes through the tap holder 123moves in an inclined posture above the body portion and the dryingfurnace.

Meanwhile, the second guiding part 122 is expanded up to the leading endof the drying furnace 160, and the second guiding part 122 is providedwith a second guiding face 122a and a second expanded part 122b, whilethe lead wire 10 is positioned on the second guiding face 122a.

As shown in FIG. 3A, The second guiding face 122a has a level lower thanthat of the first guiding face 121a by as much as the thickness of thebase paper 1111.

Further, the first inclined plate 130 is fixed on the second guidingpart 122, for moving the ferrite cores 12a and 12b toward the firstguiding part 121.

When observed in the direction of the movement of the lead wires 10, thesecond guiding face 122a of the second guiding part 122, whichcorresponds to between the leading end of the second inclined plate 140and the leading end of the drying furnace 160, is cut off, so that themoving ferrite cores 12a and 12b would be disposed above the secondguiding face 122a, as shown in FIG. 3C.

The first inclined plate 130 includes a first inclined face 131 and afirst horizontal face 132, and the second inclined plate 140 includes asecond inclined face 141 and a second horizontal face 142.

The first and second inclined plates 130 and 140 are positioned underthe lead wire 10, so that the ferrite cores can be properly moved.

Below the second inclined plate 140, there is desirably installed aferrite core rotating means 170 which includes a rubber sheet 172supported by a supporting plate 171.

The rubber sheet 172 rotates the ferrite cores when moving the ferritecore toward the adhesive of the lead wire 10.

Therefore, the rubber sheet 172 should be contacted with the ferritecore during the moving of the ferrite core. Further, the ferrite coresshould be rotatable and movable on the lead wire, and therefore, thesize and shape of the second inclined plate 140 are limited, so that thesecond inclined plate 140 would not cover the through hole uponcontacting the ferrite core.

Meanwhile, as shown in FIG. 3B, an adhesive applying means 150 which isinstalled between the first and second inclined plates 130 and 140includes: an adhesive applying wheel 152 driven by a driving shaft 151connected to a driving source (not shown); and an adhesive storage tank154 for storing an adhesive 153.

The adhesive applying wheel 152 is installed at a side of the secondguiding part 122, so that the adhesive 153 of the adhesive storage tank154 can be properly applied to the moving lead wires 10.

Meanwhile, the drying furnace 160, which is installed separated from thesecond inclined plate 140, and which is for drying the adhesive resinlayer, has an opening near the first guiding part 121, so that the leadwires 10 can pass through the drying furnace 160.

The drying furnace 160 should preferably include a heating coil 161.

Now the method for manufacturing the radial bead filter by using theabove described apparatus will be described.

In order to manufacture the radial bead filters by using the radial beadfilter manufacturing apparatus according to the present invention, firsta pair of ferrite cores 12a and 12b are fitted to each of a plurality ofthe U shaped lead wires. Then the lower portion of the lead wires 10 arepositioned on the base paper 1111 which is moved by a conveying stripmoving device 112 over the first guiding face 121a of the first guidingpart 121 of the body portion 120. Then a tape 1112 is put to fix thelead wires 10 to the base paper 1111.

As shown in FIG. 3A, the lead wires 10 which have been fixed onto thebase paper pass the first inclined plate 130. Under this condition, theferrite cores 12a and 12b which are fitted to each of the lead wires 10are made to move toward the first guiding part 121 by the first inclinedplate 130 which is fixed on the second guiding part 122.

After the ferrite cores 12a and 12b are carried to the first guidingpart 121, they pass the adhesive applying wheel 152.

Under this condition, as shown in FIG. 3B, the adhesive 153 is appliedto the lead wire 10 by the rotating action of the adhesive applyingwheel 152.

In the case where the adhesive is an epoxy resin gel, the applyingamount of the adhesive should be preferably 0.05-1.0 g, more preferably0.1-0.5 g, assuming that the diameter of the lead wire 10 is 0.6 mm.

The applying amount of the epoxy resin gel should be varied inaccordance with the moving velocity of the conveying strip 111 and therevolution speed of the adhesive applying wheel 152.

Therefore, the velocity of the conveying strip 111 and the revolutionspeed of the adhesive applying wheel 152 should be properly controlled,so that a proper adhesive applying amount can be obtained.

After applying the epoxy resin gel in the above described manner, thelead wires are made to pass through the second inclined plate 140 asshown in FIG. 3C.

Under this condition, the lead wire 10 is made to rotatingly move towardthe epoxy resin gel by the second inclined plate 140, and therefore, anadhesive resin layer is formed in the through hole of each of theferrite cores.

When the ferrite cores 12a and 12b arrive at the applied epoxy resingel, if the ferrite cores 12a and 12b rotatingly arrive, the appliedepoxy resin gel is spread between the inside of the through holes of theferrite cores 12a and 12b and the outside of the lead wire 10, with theresult that a uniform resin layer is formed.

The rotation of the ferrite cores is caused by the rubber sheet 172which is installed beneath the second inclined plate 140.

After the formation of the adhesive resin layer in the through holes 14aand 14b, the ferrite cores pass the tap holder 123 with an inclinationangle Θ, preferably 20°, with the result that the adhesive layer isdried. Consequently, as shown in FIG. 4, there is obtained a radial beadfilter in which an adhesive resin layer 180 is formed between theoutside of the lead wire 10 and the insides of the through holes 14a and14b of the ferrite cores 12a and 12b.

The ferrite cores and the lead wires are made to pass through the dryingfurnace 160 with an inclination angle Θ, preferably with 20°, so thatthe ferrite cores can be stably fixed to the adhesive layer.

When the adhesive layer which is formed between the lead wire and theferrite core is dried in the drying furnace, the drying temperatureshould be preferably 150-400° C., and more preferably 250-350° C.

The drying time should be preferably 30 second to 10 minutes, and morepreferably 1-5 minutes.

In the bead filter according to the present invention, the bondingstrength between the ferrite cores 12a and 12b and the lead wire 10becomes high. Further, the affection of the electromagneticcharacteristics of the ferrite cores by the adhesive layer is minimized.

EXAMPLE 1

An epoxy powder having a composition as shown in Table 1 below was mixedwith benzyl alcohol. Then stabilizing agents were added as shown inTable 2 below, thereby preparing epoxy resin gels having the viscositiesas shown in Table 2 below.

The mixing was carried out by applying a ball milling process.

Then the epoxy resin gels manufactured in the above described mannerwere subjected to defoaming treatments for 16 hours each.

Then by using the apparatus of FIG. 2, each of the epoxy resin gels wasapplied to each of U shaped lead wires of 0.6 mm φ in an amount of 0.4g, and then, an adhesive resin layer was formed between the inside ofthe through hole of the ferrite core and the outside of the lead wire.Then the adhesive resin layer was dried, thereby manufacturing theradial bead filters.

The ferrite core used in the above was made of a Ni--Zn ferrite(permeability: 900-1000), and its size was 3.5 (outside diameter)×6.0(length)×0.9 (inside diameter) mm.

The lead wire is an Sn--Pb coated Cu wire of 0.6 mmφ.

The drying temperature was 300° C., and the drying time was 3 minutes.

For the radial bead filters manufactured in the above described manner,impedances and the bonding strengths were measured, and the results areshown in Table 3 below.

In Table 1 below, the contents of the BPA resin show values relative tothe resin amount, and the contents of the multi functional anhydriteshow values relative to the amount of the epoxy powder.

In table 2 below, a sieve of 250 meshes was used in carrying out thefiltering.

In Table 3 below, the impedances were measured by using an impedancegain analyzer HP 4194A (at 100 MHz).

                                      TABLE 1                                     __________________________________________________________________________    Composition of Epoxy Powders                                                         Composition (wt %)                                                     Epoxy powder         Other BPA                                                                              Multi functional                                No.    Resin                                                                            SiO.sub.2                                                                        Al.sub.2 O.sub.3                                                                  Sb.sub.2 O.sub.3                                                                  ingredients                                                                         resin                                                                            anhydrite                                                                             Remark                                  __________________________________________________________________________    Inventive                                                                           1                                                                              70.0                                                                             27.0                                                                             1.0 1.0 PbO: 1.0                                                                            20 1.0     A type                                  powders                                                                             2                                                                              64.0                                                                             25.0                                                                             8.0 2.0 PbO: 0.5                                                                            40 --      adhesive                                                     SnO: 0.5                                                       3                                                                              50.0                                                                             39.0                                                                             5.0 5.0 SnO: 0.5                                                                            -- 5.0                                                                  CaO: 0.5                                                       4                                                                              53.0                                                                             40.0                                                                             5.0 2.0 tr.   -- --                                                    5                                                                              60.0                                                                             25.0                                                                             7.0 7.0 CaO: 1.0                                                                            50 3                                                     6                                                                              60.0                                                                             9.0                                                                              28.0                                                                              2.0 TiO.sub.2 : 0.5                                                                     35 2       B type                                                       PbO: 0.5         adhesive                                      7                                                                              60.0                                                                             12.0                                                                             25.0                                                                              2.0 SnO: 0.5                                                                            45 3                                                                    TiO.sub.2 : 0.5                                                8                                                                              65.0                                                                             2.0                                                                              27.0                                                                              5.0 SnO: 0.5                                                                            65 2                                                                    TiO.sub.2 : 1.0                                                9                                                                              50.0                                                                             6.0                                                                              40.0                                                                              3.0 SnO: 1.0                                                                            70 --                                                   10                                                                              70.0                                                                             5.0                                                                              22.0                                                                              2.0 TiO.sub.2 : 1.0                                                                     60 --                                              __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Epoxy Resin Gel                                                               Composition (wt %)                                                            Epoxy resin                                                                         Epoxy                                                                             Benzyl           Viscosity                                          gel No.                                                                             powder                                                                            alcohol                                                                           Stabilizer                                                                            Filtering                                                                          (cps)  Remark                                      __________________________________________________________________________    Comparative                                                                         60.0                                                                              40.0                                                                              --      X    244    Inventive                                   resin gel a                       powder 1                                    Inventive                                                                           10.0                                                                              90.0                                                                              Aceton 1.0                                                                            X    32                                                 resin gel 1                                                                   Comparative                                                                         5.0 95.0                                                                              --      X    17                                                 resin gel b                                                                   Comparative                                                                         55.0                                                                              45.0                                                                              --      O    182    Inventive                                   resin gel c                       powder 2                                    Inventive                                                                           20.0                                                                              80.0                                                                              Ethyl Alcohol 1.0                                                                     O    51                                                 resin gel 2                                                                   Comparative                                                                         2.0 98.0                                                                              --      O    11                                                 resin gel d                                                                   Comparative                                                                         70.0                                                                              30.0                                                                              Aceton 1.0                                                                            X    Unmeasurable                                                                         Inventive                                   resin gel e                       powder 3                                    Inventive                                                                           30.0                                                                              70.0                                                                              Aceton 1.0                                                                            X    84                                                 resin gel 3   Ethyl Alcohol 1.0                                               Comparative                                                                         9.0 91.0                                                                              --      X    19                                                 resin gel f                                                                   Comparative                                                                         50.0                                                                              50.0                                                                              Ethyl Alcohol 1.0                                                                     X    210    Inventive                                   resin gel g                       powder 4                                    Inventive                                                                           40.0                                                                              60.0                                                                              --      X    99                                                 resin gel 4                                                                   Comparative                                                                         4.0 96.0                                                                              Aceton 1.0                                                                            X    13                                                 resin gel h                                                                   Comparative                                                                         65.0                                                                              35.0                                                                              Ethyl Alcohol 5.0                                                                     O    Unmeasurable                                                                         Inventive                                   resin gel i                       powder 5                                    Inventive                                                                           35.0                                                                              65.0                                                                              Acenton 5.0                                                                           O    91                                                 resin gel 5                                                                   Comparative                                                                         90.0                                                                              10.0                                                                              Ethyl Alcohol 7.0                                                                     O    Unmeasurable                                       resin gel j                                                                   Comparative                                                                         82.0                                                                              18.0                                                                              Ethyl Alcohol 1.0                                                                     O    Unmeasureable                                                                        Inventive                                   resing gel k                      powder 6                                    Inventive                                                                           10.0                                                                              90.0                                                                              Acenton 8.0                                                                           X    34                                                 resin gel 6                                                                   Comparative                                                                         75.0                                                                              25.0                                                                              Ethyl Alcohol 6.0                                                                     X    Unmeasurable                                       resin gel l                                                                   Comparative                                                                         55.0                                                                              45.0                                                                              --      O    192    Inventive                                   resin gel m                       powder 7                                    Inventive                                                                           20.0                                                                              80.0                                                                              Acenton 1.0                                                                           O    36                                                 resin gel 7                                                                   Comparative                                                                         2.0 98.0                                                                              --      O    13                                                 resin gel n                                                                   Comparative                                                                         70.0                                                                              30.0                                                                              --      O    Unmeasurable                                                                         Inventive                                   resin gel o                       powder 8                                    Inventive                                                                           30.0                                                                              70.0                                                                              Ethyl Alcohol 5.0                                                                     X    84                                                 resin gel 8                                                                   Comparative                                                                         8.0 92.0                                                                              Aceton 2.0                                                                            O    12                                                 resin gel p                                                                   Comparative                                                                         60.0                                                                              40.0                                                                              --      X    231    Inventive                                   resin gel q                       powder 9                                    Inventive                                                                           40.0                                                                              60.0                                                                              Aceton 3.0                                                                            X    96                                                 resin gel 9   Ethyl Alcohol 2.0                                               Comparative                                                                         4.0 96.0                                                                              --      X    10                                                 resin gel r                                                                   Comparative                                                                         72.0                                                                              28.0                                                                              Aceton 3.0                                                                            O    Unmeasurable                                                                         Inventive                                   resin gel s                       powder 10                                   Inventive                                                                           15.0                                                                              85.0                                                                              --      O    34                                                 resin gel 10                                                                  Comparative                                                                         75.0                                                                              25.0                                                                              Ethyl Alcohol 5.0                                                                     O    Unmeasurable                                       resin gel t                                                                   __________________________________________________________________________     O: Filtering carried out.                                                     X: Filtering not carried out.                                            

In table 2, the contents of the stabilizer show values relative to themixture amount of epoxy powder and benzyl alcohol.

                                      TABLE 3                                     __________________________________________________________________________           Impedance                                                                           Bonding                                                          Bead filter No.                                                                      (Ω)                                                                           strength (kgf)                                                                        Resin gel No.                                                                         Remarks                                          __________________________________________________________________________    Comparative                                                                          86.0  1.21    Comparative                                                                           Too much resin                                   filter a             resin gel a                                                                           gel applied                                      Inventive                                                                            84.0  5.46    Iventive                                                                              --                                               filter 1             resin gel 1                                              Comparative                                                                          85.0  2.49    Comparative                                                                           --                                               filter b             resin gel b                                              Comparative                                                                          83.0  1.24    Comparative                                                                           Too much resin                                   filter c             resin gel c                                                                           gel applied                                      Inventive                                                                            87.0  5.65    Iventive                                                                              --                                               filter 2             resin gel 2                                              Comparative                                                                          88.0  2.10    Comparative                                                                           --                                               filter d             resin gel d                                              Comparative                                                                          88.0  --      Comparative                                                                           Incapable of                                     filter e             resin gel e                                                                           applying resin                                                                gel                                              Inventive                                                                            87.0  4.60    Iventive                                                                              --                                               filter 3             resin gel 3                                              Comparative                                                                          86.0  2.98    Comparative                                                                           --                                               filter f             resin gel f                                              Comparative                                                                          79.0  1.78    Comparative                                                                           --                                               filter g             resin gel g                                              Inventive                                                                            82.0  4.32    Iventive                                                                              --                                               filter 4             resin gel 4                                              Comparative                                                                          84.0  2.42    Comparative                                                                           --                                               filter h             resin gel h                                              Comparative                                                                          80.0  --      Comparative                                                                           Incapable of                                     filter i             resin gel i                                                                           applying resin                                                                gel                                              Inventive                                                                            84.0  3.98    Iventive                                                                              --                                               filter 5             resin gel 5                                              Comparative                                                                          86.0  --      Comparative                                                                           Incapable of                                     filter j             resin gel j                                                                           applying resin                                                                gel                                              Comparative                                                                          74.0  --      Comparative                                                                           Incapable of                                     filter k             resin gel k                                                                           applying resin                                                                gel                                              Inventive                                                                            78.0  3.14    Iventive                                                                              --                                               filter 6             resin gel 6                                              Comparative                                                                          70.0  --      Comparative                                                                           Incapable of                                     filter l             resin gel l                                                                           applying resin                                                                gel                                              Comparative                                                                          68.0  2.22    Comparative                                                                           --                                               filter m             resin gel m                                              Inventive                                                                            74.0  5.47    Iventive                                                                              --                                               filter 7             resin gel 7                                              Comparative                                                                          74.0  2.42    Comparative                                                                           --                                               filter n             resin gel n                                              Comparative                                                                          61.0  --      Comparative                                                                           Incapable of                                     filter o             resin gel o                                                                           applying resin                                                                gel                                              Inventive                                                                            75.0  4.71    Iventive                                                                              --                                               filter 8             resin gel 8                                              Comparative                                                                          74.0  2.83    Comparative                                                                           --                                               filter p             resin gel p                                              Comparative                                                                          79.0  1.22    Comparative                                                                           --                                               filter q             resin gel q                                              Inventive                                                                            74.0  4.39    Iventive                                                                              --                                               filter 9             resin gel 9                                              Comparative                                                                          72.0  2.11    Comparative                                                                           --                                               filter r             resin gel r                                              Comparative                                                                          74.0  --      Comparative                                                                           Incapable of                                     filter s             resin gel s                                                                           applying resin                                                                gel                                              Inventive                                                                            76.0  5.13    Iventive                                                                              --                                               filter 10            resin gel 10                                             Comparative                                                                          75.0  --      Comparative                                                                           Incapable of                                     filter t             resin gel t                                                                           applying resin                                                                gel                                              Conventional                                                                         63.91 5.10    Resin based                                                                           --                                               filter 1             adhesive                                                 Conventional                                                                         69.726                                                                              4.71    Phenol based                                                                          --                                               filter 2             adhesive                                                 __________________________________________________________________________

As shown in Table 3 above, the bead filters according to the presentinvention show impedances equal to or superior over the comparativefilters or the conventional filters, while the bonding strength of thefilters of the present invention is superior over the comparativefilters and the conventional filters.

EXAMPLE 2

Bead filters were manufactured in the same manner as those of theinventive filters 1, 3, 6 and 9 of Table 3 above, except that thefiltering was carried out by using a sieve of 325 meshes prior todefoaming the resin gels.

For the bead filters manufactured in the above described manner,impedances and bonding strengths were measured, and the measured resultsare shown in Table 4 below.

                  TABLE 4                                                         ______________________________________                                        Bead filter No.                                                                        Filtering.                                                                              Impedance (Ω).                                                                      Bonding strength (kgf)                         ______________________________________                                        Inventive                                                                            1     X         84        5.46                                         filter       O         83        5.55                                                3     X         87        4.60                                                      O         88        4.91                                                6     X         78        3.14                                                      O         77        4.11                                                9     X         74        4.39                                                      O         75        4.42                                         ______________________________________                                         O: Filtering carried out.                                                     X: Filtering not carried out.                                            

As shown in Table 4 above, in the case where the resin gels werefiltered prior to defoaming, the bonding strength was improved.

EXAMPLE 3

Bead filters were manufactured in the same manner as that of theinventive filter 1 of Table 3, except that the adhesive resin layer wasdried for 3 minutes, and that the drying temperatures were varied asshown in Table 5 below.

For the bead filters manufactured in the above described manner,impedances and bonding strengths were measured, and the measured resultsare shown in Table 5 below.

                  TABLE 5                                                         ______________________________________                                                Drying                                                                Bead filter                                                                           temperature                                                                             Impedance                                                                              Bonding                                            No.     (° C.)                                                                           (Ω)                                                                              strength (kgf).                                                                        Remarks                                   ______________________________________                                        Comparative                                                                            50       90       0.15     Not dried.                                filter u                                                                      Comparative                                                                           100       89       0.75     Surface                                   filter v                            only dried.                               Comparative                                                                           120       90       1.25     Imperfectly                               filter w                            dried.                                    Inventive                                                                             200       87       3.99     --                                        filter 10                                                                     Inventive                                                                             300       88       5.46     --                                        filter 11                                                                     Inventive                                                                             400       82       3.89     Partial                                   filter 12                           carbonization                                                                 occurred.                                 Comparative                                                                           500       80       2.36     Epoxy                                     filter x                            carbonized.                               ______________________________________                                    

As shown in Table 5 above, when carried out the drying of the adhesiveresin layer according to the present invention, the bonding strengthswere superior.

EXAMPLE 4

Bead filters were manufactured in the same manner as that of theinventive filter 1 of Table 3 above, except that the drying conditionsfor the adhesive resin layer were varied as shown in Table 6 below.

For the bead filters manufactured in the above described manner,impedances and bonding strengths were measured, and the measured resultsare shown in Table 6 below.

                                      TABLE 6                                     __________________________________________________________________________           Drying conditions.                                                            Pre-heating                                                                   part  Drying part                                                                         Cooling part                                                                             Bonding                                                Temp                                                                             Time                                                                             Temp                                                                             Time                                                                             Temp                                                                             Time                                                                             impedance                                                                          strength                                        Bead filter No.                                                                      (° C.)                                                                    (min)                                                                            (° C.)                                                                    (min)                                                                            (° C.)                                                                    (min)                                                                            (Ω)                                                                          (kgf)                                                                              Remarks                                    __________________________________________________________________________    Inventive                                                                           1                                                                              -- -- 300                                                                              3  -- -- 88   5.46 1-step drying                              filter                             method                                          13                                                                              200                                                                              1.0                                                                              300                                                                              2.0                                                                              -- -- 87   5.84 2-step drying                                                                 zone method                                     14                                                                              200                                                                              1.0                                                                              350                                                                              2.0                                                                              -- -- 86   5.72                                                 15                                                                              100                                                                              0.5                                                                              300                                                                              1.5                                                                              200                                                                              1.0                                                                              86   6.01                                                 16                                                                              150                                                                              0.5                                                                              350                                                                              1.5                                                                              250                                                                              1.0                                                                              86   5.92 3-step drying                                                                 zone method                                __________________________________________________________________________

As shown in Table 6 above, the 2-step and 3-step drying zone methodsshow superior bonding strength compared with the 1 step drying method.

According to the present invention as described above, the radial beadfilters having superior electromagnetic characteristics and superiorbonding strengths can be continuously manufactured with a simpleprocess.

What is claimed is:
 1. An apparatus for manufacturing a bead filterincluding a lead wire and a pair of ferrite cores each having a throughhole for eliminating electromagnetic interference in electronicapparatus, comprising:a conveyor (110) for moving lead wires insertedinto ferrite cores; a body (120) for guiding and supporting saidconveyor (110); first and second inclined plates (130) and (140)attached to said body (120), for moving said ferrite cores (12a) and(12b) in opposite directions; a core rotator (170) installed beneathsaid second inclined plate (140) for rotating said cores when said coresare carried by said second inclined plate (140); an adhesive applicator(150) installed between said first and second inclined plates (130) and(140) for applying adhesive to said lead wires; and a drying furnace(160) installed at a side of said body portion (120) adjacently to saidsecond inclined plate (140) to receive and dry the adhesive applied tosaid lead wires.
 2. The apparatus as claimed in claim 1, wherein:eachlead wire is U-shaped for fitting a pair of said ferrite cores to saidlead wire; said conveyor (110) includes: a conveying strip (111)composed of a base paper (11111) and a tape (1112); and a conveyingstrip moving device (112) for moving said conveying strip (111); saidbody (120) includes: a first guiding part (121) having a first expandedpart (121b) and a first guiding face (121a) for guiding said conveyingstrip (111); and a second guiding part (122) having a second guidingface (122a) and a second expanded part (122b); said second guiding face(122a) between the leading end of said second inclined plate (140) andsaid drying furnace (160) as observed in the lead wire conveyingdirection is cut open so that the moving cores are positioned over thecut portion with certain intervals; said first inclined plate (130)includes a first inclined face (131) and a first horizontal face (132);said second inclined plate (140) includes a second inclined face (141)and a second horizontal face (142); said core rotator (170) includes arubber sheet (172); said adhesive applicator (150) includes an applyingwheel (152) for applying the adhesive from an adhesive storage tank(154) to said lead wires; and said drying furnace (160) is open on theside of said first guiding part (121), and includes a heating coil(161).
 3. The apparatus as claimed in claim 2, wherein:said base paper(1111) and said tape (1112) are respectively provided with a pluralityof pin holes (1112a); said conveying strip moving device (112) includes:one or more gear rollers (1121), and one or more pin rollers (1122) eachincluding a plurality of pins (1122a); said first guiding face (121a)includes a plurality of pin holes for accommodating said pins (1122a) ofsaid pin rollers (1122); a tap holder (123) for inclining said conveyingstrip (111) is formed at a position on said first guiding part (121) andsaid first expanded part (121b) between the rear end of said secondinclined plate (140) and the leading end of said drying furnace (160);said first guiding face (121a) of said first guiding part (121) betweenthe leading end of said tap holder (123) and the rear end of said dryingfurnace (160) has a downward inclination toward a pair of said ferritecores by a certain amount of angular degrees; and a conveying stripretaining slot (123a) for allowing a passthrough of said conveying strip(111) is formed between said tap holder (123) and said first guidingface (121a).
 4. The apparatus as claimed in claim 2, wherein said tapeis a thermal tape.
 5. The apparatus as claimed in claim 3, wherein saidfirst guiding face (121a) has a downward inclination of 20°.
 6. Theapparatus as claimed in claim 3, wherein one or more of conveying stripguides (113) are formed on said first expanded part (121b) of said firstguiding part (121).
 7. The apparatus as claimed in claim 6, wherein saidtape is a thermal tape.